1. Field of the Invention
This invention relates to a method of dicing a semiconductor wafer, and it relates, more particularly, to an improvement in the method of dicing wafers made of a III-V compound semiconductor material.
2. Description of the Prior Art
Recently, semiconductor substrates made of a III-V compound semiconductor material such as GaAs, GaP and InP have been mass-produced for semiconductor devices, in addition to silicon. The substrates made of a III-V compound semiconductor material are weak in mechanical strength as compared to the silicon, and such weakness is overcome technically.
One or a plurality of kinds selected from a group consisting of passive and active elements such as a resistor and transistor are made into an element. A plurality of such elements are fabricated in a wafer of a III-V compound semiconductor material in the same way prepared for a wafer made of silicon.
In the course of production, dicing lines are marked between the boundary lines of chips 3 by using, for instance, a diffusion method. A wafer will be separated to the chips 3 by a specific method.
Of dicing processes, the following three methods are well known in the art. These are the diamond scribing method, the diamond blade method and the dicing saw method. For each method implemented, it is necessary to minimize the distance of a groove between chips 3 in terms of maximum available area and to minimize also the damage to the chips 3, for instance, to prevent so-called chipping 2 that causes a crack and breakage as shown in FIG. 2A.
Among the three methods, each are used according to its specific purpose. In the dicing saw method, the thin wheel, in the tip of which diamond particles are sintered, dices the wafer from the X- and Y-axis directions (see FIG. 2A) in the width of 20-40 .mu.m on the wafer with a high speed of 10,000 to 50,000 rpm. The depth of the groove to be cut can be chosen freely and a complete cut (through-cut) is also possible.
The advantages of the dicing saw method lies in the fact that the method provides a stable width of cut in the groove and a deep groove of cut. Further, there are little cracks or chipping 2 caused, and the cutting takes places at a high speed, and is thus preferable in a mass-production. This dicing saw method is suitable for dicing the wafer having the width of 400 .mu.m through 600 .mu.m.
In the diamond scribing method, a wafer to be processed is fixed by means of a vacuum chuck or static chuck, and the groove of cut is formed by a diamond cutter with a predetermined load from the directions of X- and Y-axes as shown in FIG. 1B. After the depth of cut in the groove is formed at a rather shallow depth of, say, 50 .mu.m, the wafer will be separated into chips 3 by applying a mechanical force by means of a rubber roller or the like. In this method, there is a drawback that the chipping 2 and cracks are likely to occur. Notwithstanding, the apparatus used in this method is simple and inexpensive.
In the diamond blade method similar to the diamond scribing method, the groove of cut is formed at a predetermined position by a diamond cutter with a certain load from the directions of X- and Y-axes. Then, the wafer is usually cut through by moving the blade made from diamond as shown in FIG. 2B.
As shown in FIG. 2A, an orientation flat 6 is usually provided in a circular wafer of a III-V compound semiconductor material. A chip 3 whose typical dimension is 0.3 mm and 0.5 mm of rectangular shape is fabricated in the wafer.
In the diamond scribing method using the cleaving characteristics, there are cases where an incomplete breakage occurs though the width of groove can be made as small as about 40 .mu.m or less. When dicing the wafer of a III-V semiconductor material with this method to obtain chips 3, it is especially hard to cut the chip in a parallel direction with a longer side of the rectangular chip, namely in the direction parallel to a cleaving direction. This will cause a chip pair 1 or a broken chip pair 7 shown in FIG. 1, thus affecting to lower the yield.
In the diamond blade method used to dice the wafer of a III-V semiconductor material as shown in FIG. 3, there are cases where chipping 2 shown in FIG. 2A and FIG. 3 often occurs even though the method can perform to cut through the wafer completely. For this reason, the width of the dicing line should be formed as wide as about 100 .mu.m. This requires the area occupied by a chip 3 to be greater. FIG. 2A, and FIG. 2B show the occurrence of chipping 2. FIG. 3 shows an enlarged view thereof.